Progressive miniaturization of feature sizes in circuit elements has improved the performance and increased the functional capability of integrated circuits. Fin-type field effect transistors (FinFET's) are low-power, high speed devices that can be more densely packed on a substrate than planar transistors. A conventional FinFET structure includes a narrow vertical fin of single crystal semiconductor material and a gate electrode that intersects a channel region of the fin. The gate electrode is isolated electrically from the fin by a thin dielectric layer. Flanking the central channel region on opposite ends of the vertical fin are source/drain regions. Because of the fabrication process, the fin has a width that is less than the minimum lithographic dimension and a relatively high aspect ratio.
After the gate electrode is formed, the gate dielectric covers the entire sidewall of the fin. Consequently, the gate dielectric must be removed from the exposed ends of the fin to create the source/drain regions by introducing a dopant concentration into the opposite ends of the fin. The dopant concentration may be introduced into the fin by angled ion implantation or by gas phase diffusion doping. However, the stage in the fabrication process that introduces the dopant into the source/drain regions also modifies the doping in the gate electrode because the gate electrode is exposed to the process introducing the dopant into the opposite ends of the fin. Consequently, the gate doping, and hence the work function of the gate electrode, is strongly coupled with the process that dopes the source/drain regions and is altered by the source/drain doping process. For example, the gate work function in an n-channel FinFET may be highly influenced by the high concentration n-type doping of the source/drain regions because of the additional concentration of n-type dopant introduced into the gate electrode by the process doping the source/drain regions.
What is needed, therefore, is a semiconductor structure in which a dopant concentration may be introduced into the fin of a FinFET to form source/drain regions without co-doping the gate electrode and methods of fabricating such semiconductor structures that overcome the various disadvantages of conventional semiconductor structures and conventional methods of manufacturing such semiconductor structures.